arXiv subjects

Gaurava K. Jaisawal

Publications and source records attributed to Gaurava K. Jaisawal.

76 records · Page 5Linked to original sources

arXiv2014

Suzaku Observation of Be/X-ray Binary Pulsar EXO 2030+375

In this paper we study the timing and spectral properties of Be/X-ray binary pulsar EXO 2030+375 using a $Suzaku$ observation on 2012 May 23, during a less intense Type I outburst. Pulsations were clearly detected in the X-ray light curves at a barycentric period of 41.2852 s which suggests that the pulsar is spinning-up. The pulse profiles were found to be peculiar e.g. unlike that obtained from the earlier Suzaku observation on 2007 May 14. A single-peaked narrow profile at soft X-rays (0.5-10 keV range) changed to a double-peaked broad profile in 12-55 keV energy range and again reverted back to a smooth single-peaked profile at hard X-rays (55-70 keV range). The 1.0-100.0 keV broad-band spectrum of the pulsar was found to be well described by three continuum models such as (i) a partial covering high energy cut-off power-law model, (ii) a partially absorbed power-law with high-energy exponential rolloff and (iii) a partial covering Negative and Positive power law with EXponential (NPEX) continuum model. Unlike earlier Suzaku observation during which several low energy emission lines were detected, a weak and narrow Iron K_alpha emission line at 6.4 keV was only present in the pulsar spectrum during the 2012 May outburst. Non-detection of any absorption like feature in 1-100 keV energy range supports the claim of absence of cyclotron resonance scattering feature in EXO 2030+375 from earlier Suzaku observation. Pulse-phase resolved spectroscopy revealed the presence of additional dense matter causing the absence of second peak from the soft X-ray pulse profiles. The details of the results are described in the paper.

astro-ph.SR↗

arXiv2013

Possible detection of a cyclotron resonance scattering feature in the X-ray pulsar 4U 1909+07

We present timing and broad-band spectral studies of the high mass X-ray binary pulsar 4U 1909+07 using data from Suzaku observation during 2010 November 2-3. The pulse period of the pulsar is estimated to be 604.11+/-0.14 s. Pulsations are seen in the X-ray light curve up to ~70 keV. The pulse profile is found to be strongly energy-dependent: a complex, multi-peaked structure at low energy that becomes a simple single peak at higher energy. We found that the 1-70 keV pulse averaged continuum can be fitted by the sum of a black body and a partial covering Negative and Positive power-law with EXponential cutoff (NPEX) model. A weak iron fluorescence emission line at 6.4 keV was detected in the spectrum. An absorption like feature at ~44 keV was clearly seen in the residue of the spectral fitting, independent of the continuum model adopted. To check the possible presence of a CRSF in the spectrum, we normalized the pulsar spectrum with the spectrum of the Crab Nebula. The resulting Crab ratio also showed a clear dip centered at ~44 keV. We performed statistical tests on the residue of the spectral fitting and also on the Crab spectral ratio to determine the significance of the absorption like feature and identified it as a CRSF of the pulsar. We estimated the corresponding surface magnetic field of the pulsar to be 3.8 x 10^12 Gauss.

astro-ph.HE↗

arXiv2013

Detection of a variable QPO at ~41 mHz in the Be/X-ray transient pulsar 4U 0115+634

We report the detection of quasi-periodic oscillation (QPO) at ~41 mHz in the transient high-mass Be/X-ray binary pulsar 4U~0115+634 using data from the Rossi X-Ray Timing Explorer (RXTE) observatory. The observations used in the present work were carried out during X-ray outbursts in 1999 March-April, 2004 September-October and 2008 March-April. This frequency of the newly detected QPO was found to vary in 27-46 mHz range. This ~41 mHz QPO was detected in four of the 36 pointed RXTE Proportional Counter Array (PCA) observations during 1999 outburst where as during 2004 and 2008 outbursts, it was detected in four and three times out of 33 and 26 observations, respectively. Though QPOs at ~2 mHz, and ~62 mHz were reported earlier, the ~41 mHz QPO and its first harmonic were detected for the first time in this pulsar. There are three RXTE/PCA observations where multiple QPOs were detected in the power density spectrum of 4U~0115+634. Simultaneous presence of multiple QPOs is rarely seen in accretion powered X-ray pulsars. Spectral analysis of all the pointed RXTE/PCA observations revealed that the 3-30 keV energy spectrum was well described by Negative and Positive Power-law with EXponential cutoff (NPEX) continuum model along with interstellar absorption and cyclotron absorption components. During the three X-ray outbursts, however, no systematic variation in any of the spectral parameters other than the earlier reported anti-correlation between cyclotron absorption energy and luminosity was seen. Presence of any systematic variation of QPO frequency and rms of QPO with source flux were also investigated yielding negative results.

astro-ph.SR↗

arXiv2013

Timing and Spectral properties of Be/X-ray pulsar EXO 2030+375 during a Type I outburst

We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy dependent pulse profiles were clearly detected up to ~100 keV. Narrow dips are seen in the profiles up to ~70 keV. Presence of prominent dips at several phases in the profiles up to such high energy ranges were not seen before. At higher energies, these dips gradually disappeared and the profile appeared single-peaked. The 1.0-200.0 keV broad-band spectrum is found to be well described by a partial covering high energy cut-off power-law model. Several low energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with above continuum model yielding similar parameter values. The partial covering with partially ionized absorber resulted into marginally better fit. The spectral fitting did not require any cyclotron feature in the best fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of additional column density was estimated to be high compared to other pulse phases. While using partially ionized absorber, the value of ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.

astro-ph.HE↗